A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Health Systems Management (MHSM) of Mzumbe University.This study examined adverse health effects of second hand tobacco smoke among under five children. The study sample consisted of 200 respondents, 100 exposed and 100 non-exposed group. Data were collected through questionnaire and interviews, collected data were entered in MS-Excel and correlation analysis was performed using SPSS computer software. The study findings indicated that 56% of respondents have attained primary school education, 22.5% secondary education,56% of respondents were in age between 21-30 years old, 21% aged between 31-40 years old and 16% aged between 15-20 year old. The study results also indicated 58.5% of under five children were female and 41.5% were male. Additionally, 24.5% of them were at age of 0-6 months, followed by 23% of those aged between 14-26 months and 20.5% aged between 7-13 months. The study findings also revealed the significant relationship/association between second hand smoke and occurrence of sudden infant death syndrome, ear infections, childhood asthma, eye irritation, wheezing, chest tightness, low birth weight, and coughing among under five children whereby had statistically similar and significant (P<0.05), with exception of lung infections where results indicated no association between outcome and SHS, the PV was greater than 0.05. Furthermore, findings indicated that 44% of children under age 5 are exposed to more than 5 cigarettes smoked by member(s) of household per day, while 41% were exposed to 3 to 5 cigarettes per day. The study also found 98% of smokers are men compared to smoking mothers who are only 2%. 55% of respondents smoke in same room with under five children while other 45% avoid smoking in the same room with under five children. More than half (54%) of respondents agreed that they smoke on environment close to under five children and other 46% smoke far from children. The results in this study indicates high rate of adverse health effects of SHS among under five children, therefore it recommends 100% smoke free environment at home by family members. Also successfully elimination exposure to tobacco smoke requires efforts at all level from global and household level.